1. Field of the Invention
The present invention is generally related to composite materials, and more particularly to composite materials with electron-donating and electron-accepting property, their forming method, and application in photovoltaic devices.
2. Description of the Prior Art
In conventional solid-state solar cells, electron-hole pairs are created by light absorption in a semiconductor, with charge separation and collection accomplished under the influence of electric fields within the semiconductor. However, extensive usage of inorganic photovoltaic devices is limited due to the high costs by the fabrication procedures involving elevated temperature, high vacuum, and numerous lithographic steps. The development of new types of photovoltaic devices has been a growing attention owing to the public awareness of the shortage and running out of Earth's oil reserve.
Large-area thin-film photovoltaic devices based on conjugated polymer are of great interest in the last couple of years, because the availability of a soluble semiconductor not only opened the way towards cheaper processing via numerous coating methods, but also made it possible to investigate blends with other semiconductors while maintaining the advantages of solution processing. Mechanical flexibility and low weight of polymer materials make them more attractive for photovoltaic applications although devices fabricated based on conjugated polymer have been found to have low conversion efficiencies.
At present, the nanoparticle/polymer composites for photovoltaic devices are prepared by blending semiconducting nanoparticles with conducting polymers in solvent. The nanoparticles are randomly distributed in the polymer matrix. In order for the nanoparticles in the polymer matrix to form a highly connected network, usually the nanoparticles have to be in high concentration. A coagulation problem of the composites often occurs from high concentration of nanoparticles and reduces the interfacial actions between the polymer and nanoparticle that results in a decreased in the quantum efficiency. Therefore, new composite materials are still needed to eliminate coagulation problem, to increase interfacial actions between nanoparticle and polymer, and to be fabricated into high efficiency photovoltaic devices.